The Department of Immunology of TSRI is composed of 54 full-time staff members and more than 75 research associates (post-doctoralfellows). The research interests of this department encompass many of the diverse areas that are broadly classified as Immunology. A common theme in nearly all of the research programs centers around investigations of protein-protein interactions. These studies range from studies of antigen-antibody interactions to determination of how cell surface receptors mediate cell-cell interactions. In many of the laboratories as noted below sufficient quantities of the requisite proteins are available from either recombinant or - natural sources to perform rigorous analysis of protein-protein interactions. There is a BIA core instrument on the TSRI campus in the Department of Molecular Biology housed in a building adjacent to the Immunology department This instrument is heavily used by several individuals. Although the major users of the existing BIA core do their best to make the equipment available, on a practical basis access is severely restricted. We do not anticipate current usage of the existing equipment to decrease so we are not optimistic about increased access in the future. Therefore we believe there is a strong justification for purchase of a BIA core instrument dedicated for usage within the Department of Immunology. Nine members of the staff of the Department of Immunology of The Scripps Research Institute, all of whom are laboratory heads and independently funded by MH grants, will derive substantial benefit from the acquisition of the Pharmacia BIAcore instrument. More than 50 scientists are represented within these nine independent research units.